Centrifugal pump, in particular a spirally-housed centrifugal pump for a heat exchange medium

ABSTRACT

In a centrifugal pump—in particular a spiral-casing centrifugal pump—for a heat carrier medium, comprising a spiral casing ( 14 ) having an impeller ( 40 ), a casing cover ( 18 ) and an associated casing attachment portion ( 34 ) for a pump shaft ( 35, 36, 36   a ) provided with a shaft bearing ( 76, 76   a ) near the spiral casing ( 14 ) and a shaft seal ( 56 ) disposed at a spacing in relation to the shaft bearing in a sealing chamber ( 48 ), parts of the casing cover ( 18 ) are a bearing cup ( 28 ) accommodating the shaft bearing ( 76, 76   a ), a tubular portion ( 32 ) surrounding the pump shaft ( 35, 36, 36   a ) as a heat barrier and support ribs ( 56 ) or the like profile elements arranged at a spacing relative to each other in the peripheral direction. The bearing cup ( 28 ) is held at an axial spacing towards the impeller ( 40 ) by the tubular portion ( 32 ) surrounding the pump shaft ( 35, 36, 36   a ), and the casing attachment portion ( 34 ) attached to the casing cover ( 18 ) or an edge ring ( 30 ) carried by the support ribs ( 26 ) thereof delimits the sealing chamber ( 48 ) for the shaft seal ( 56 ).

The invention concerns a centrifugal pump—in particular a spiral-casing centrifugal pump—for a heat carrier medium, comprising a spiral casing having an impeller, a casing cover and an associated casing attachment portion for a pump shaft provided with a shaft bearing near the spiral casing and a shaft seal disposed at a spacing in relation to the shaft bearing in a sealing chamber.

Such centrifugal pumps are described by way of example in a prospectus from the present applicants in relation to the range NHT for heat carrier purposes up to 350° C. A spiral casing for an impeller is connected to a bearing casing by means of a throttle section having external ribs. The impeller is fixed at one end of a pump shaft which extends in the throttle section. Arranged between the throttle section and the impeller is a plain bearing of silicon carbide and arranged downstream of the throttle section is a sliding ring seal which is followed by a rolling bearing. This arrangement involves a horizontal spiral-casing centrifugal pump of a process type of structure which is single-stage in terms of intake flow. The pump-side silicon carbide plain bearing is lubricated by the fluid being delivered, while used at the drive side is a grease-lubricated grooved-type ball bearing.

In consideration of that state of the art, the inventor set himself the aim of providing a centrifugal pump of the kind set forth in the opening part of this specification, which is simple to manufacture and which can be inexpensively and particularly well used.

That object is attained by the teaching of the independent claim; the appendant claims set forth advantageous developments. In addition the scope of the invention embraces all combinations comprising at least two of the features disclosed in the description, the drawing and/or the claims.

In accordance with the invention a bearing cup accommodating the shaft bearing, a tubular portion surrounding the pump shaft as a heat barrier and so-called support ribs or the like profile elements arranged at a spacing relative to each other in the peripheral direction are parts of the casing cover. Those features permit the pump to be of a simple structure with only two pressure-bearing parts for the bearing carrier casing—comprising the casing cover and the casing attachment portion—as well as a particularly high level of stability for the bearing carrier casing.

In addition the bearing cup is to be held at an axial spacing towards the impeller by the tubular portion which surrounds the pump shaft.

The sealing chamber for the shaft seal is advantageously delimited by the casing attachment portion which is preferably joined to the casing cover or an edge ring which is carried by the support ribs thereof and which surrounds the longitudinal axis of the pump; the edge ring is connected to and preferably integrally formed on the support ribs at their ends remote from the base region of the casing cover.

Disposed between the spiral casing and the above-mentioned sealing chamber is a latticework-like or trussing-like rib arrangement comprising those support ribs which are to be inclined towards the longitudinal axis from the spiral casing at a preferred angle of between 40° and 45° and—at a radial spacing relative to each other—surround the bearing cup and the heat barrier and form jointly therewith the casing cover.

For that purpose it has proven to be desirable for the cross-sectional height of the support ribs which preferably extend in axial planes which pass radially through the longitudinal axis of the pump to be caused to increase towards the sliding ring seal in order to enhance the level of stability and minimise heat losses.

In accordance with a further feature of the invention the sealing chamber is to adjoin the shaft bearing. Inter alia that ensures an adequate supply of lubricating medium to the bearing. In addition the bearing contributes to circulation of the medium in the sealing chamber for flushing and cooling the seal.

In order to enlarge the use of the centrifugal pump according to the invention and the combination options thereof, it is possible to arrange on the casing cover at least one abutment stage or step directed away from the spiral casing, for a further part of the pump; that abutment step should preferably be a front ring which is formed on the casing cover. An associated pump part can moreover be a spacer which extends around the bearing carrier casing and which abuts against the abutment step or steps or the front ring and to which a motor is attached.

It has proven to be desirable for the abutment step or the front ring to be arranged to project from an annular flange which extends around the support ribs and which is mounted to the transition thereof to a base region of the casing cover.

The scope of the invention includes a centrifugal pump with a sealing ring of the shaft seal—in the form of a sliding ring seal—, the sealing ring extending therearound on a counterpart ring provided at the casing side; the counterpart ring is arranged for the sealing ring in a shaped stub portion of the casing attachment portion, the stub portion projecting axially into the sealing chamber. At last one opening or passage which is inclined with respect to the longitudinal axis of the pump and with a closure screw for closing it is to be associated with the stub portion—which is of an axial length approximately corresponding to half the axial length of the sealing chamber—; the longitudinal axis of the passage advantageously delimits an angle of about 45° with the longitudinal axis of the pump. Thus the sliding ring seal is advanced within the sealing chamber in order to make available sufficient space for collecting air or outgassings of the delivery medium—in particular when the arrangement is positioned vertically. The described arrangement of the passage with the closure screw easily permits complete venting of the sealing chamber both when the pump is positioned horizontally and also vertically.

The frictional heat of the sliding ring seal is desirably dissipated to the surroundings by virtue of a large surface area of the surrounding sealing chamber and a large volume of fluid in the sealing chamber.

In accordance with the invention the shaft bearing is in the form of a plain bearing with a ratio of the length of the bearing bush to the diameter of the pump shaft of between about 1.5 and 2.0, preferably about 1.8. In addition the bearing bush of the plain bearing should be designed to be dismantled. Advantageously the plain bearing, as viewed from the impeller, is disposed behind the heat barrier, which contributes to simplicity of possible fixing and also contributes to the heat barrier being of a desirable design configuration.

In order to achieve a low level of heat conduction from the spiral casing to the sealing chamber, a small cross-section and a long length of the tubular portion, which is in the form of the heat barrier, of the casing cover has proven to be desirable. That can be implemented particularly well with the specified bearing arrangement.

The positioning of the impeller-side bearing behind the heat barrier means that the delivery medium which serves as a lubricating agent is at a lower temperature at that location than in the pump casing. As a result it is of higher viscosity, which is advantageous for the lubricating capability. In addition the vapor pressure of the medium at that location is markedly lower than in the pump casing, thereby minimising the risk of the bearing running dry.

It has proven to be desirable for the plain bearing or the bearing bush thereof, for fixing purposes, to be surrounded approximately at the longitudinal center thereof on the outside by a clamping or tolerance ring which engages into the bearing cup. The width of the clamping or tolerance ring should correspond to a fraction of the length of the bearing bush, for example between a fifth and a sixth of the length of the bearing bush. That provides for easy (dis-)mantling as well as compensation for alignment errors by virtue of tilting mobility.

There are a number of design configurations of the plain bearing, in accordance with the invention. In one case the plain bearing includes an inner bearing sleeve which is surrounded by a bearing bush at the bearing cup side. In that case the pump shaft is surrounded within the plain bearing by at least one tolerance ring which engages into the pump shaft. In particular an inward tolerance ring should be provided on each of the two sides of the outer tolerance ring which engages into the bearing cup—as viewed in longitudinal section of the centrifugal pump—, the inward tolerance ring engaging into the pump shaft. The bearing sleeve and the bearing bush are preferably made from silicon carbide.

Another design configuration in accordance with the invention involves a plain bearing with a bearing bush at the bearing cup side, the bearing bush including a slidable internal peripheral surface portion which extends around the pump shaft. In that case the dismantleable plain bearing bush is preferably provided with an inner carbon coating. The bush runs on a hardened shaft or a hardened shaft portion. Fixing is effected by a centrally disposed outer tolerance ring, as already mentioned.

In accordance with a further feature of the invention the sliding ring seal extends around a shaft sleeve at the shaft side, wherein at least one O-ring is provided between the shaft sleeve and the pump shaft. That arrangement, in a construction which is relieved of load, permits assembly of the sliding ring seal from the impeller side, which is desirable in particular when the shaft is in the form of a plug-in shaft.

In accordance with another feature of the invention arranged in the casing attachment portion at an axial spacing relative to the sliding ring seal outside the sealing chamber is a rearward shaft bearing for the pump shaft; at least one hollow space can also be provided in the casing attachment portion between the sealing chamber and the shaft bearing.

In a particular configuration the pump shaft is in the form of a plug-in shaft with clamping ring.

By virtue of the described different design configurations of the plain bearing, in combination with the three types of structure:

pump with main plate and coupling;

pump of a block-type structure; and

pump of an in-line type of structure

there are at least six structural variants for the centrifugal pump according to the invention.

Further advantages, features and details of the invention will be apparent from the description hereinafter of preferred embodiments and with reference to the drawing in which:

FIGS. 1 and 8 each show a perspective view of different embodiments of a centrifugal pump according to the invention for heat carrier media,

FIG. 2 shows an end view of the FIG. 1 structure,

FIG. 3 shows a partial longitudinal section through FIG. 2 along line III-III therein,

FIG. 4 shows a view in longitudinal section on an enlarged scale through the pump in FIG. 2 taken along line IV-IV therein,

FIG. 5 shows a view on an enlarged scale of a part of the FIG. 4 structure,

FIG. 6 shows a longitudinal section corresponding to FIG. 4 through another embodiment of the pump shown in FIG. 1,

FIG. 7 shows a view on an enlarged scale of a portion of the FIG. 6 structure,

FIG. 9 shows an end view of the FIG. 8 structure,

FIG. 10 shows a perspective view of a casing cover of the pump,

FIG. 11 shows a view on an enlarged scale through the pump of FIGS. 8 and 9 taken along line XI-XI in FIG. 9,

FIG. 12 shows a partial longitudinal section on an enlarged scale in relation to FIG. 11 taken along line XII-XII in FIG. 9,

FIGS. 13 and 14 show different perspective views of a part of a further embodiment of a centrifugal pump according to the invention,

FIG. 15 shows an end view of the structure shown in FIGS. 13 and 14,

FIG. 16 shows a partial longitudinal section through the pump of FIGS. 13 through 15 taken along line XVI-XVI in FIG. 15, and

FIG. 17 shows a partial section on an enlarged scale in relation to FIG. 16 through that pump taken along line XVII-XVII in FIG. 15.

A spiral-casing centrifugal pump 10, on a volute or spiral casing 14 provided with connecting flanges 12, 12 _(a),—with the interposition of seals (not shown)—has a bearing carrier casing 16 which includes a casing cover 18 with a casing attachment portion 34 fitted thereto.

The casing cover 18 is provided with an annular flange 21 which projects from a dish-like base region 20 and through which pass connecting screws 24, on a front ring 22 which is formed on the annular flange 21 and which forms an abutment step; the connecting screws 24 are fitted into sleeve ribs 15 which are formed in axis-parallel relationship externally on a peripheral wall 13 of the spiral casing 14, the peripheral wall engaging over the dish wall 19, and the screws 24 centeringly connect the casing cover 18 to the spiral casing 14.

Formed on the casing cover 18 or the base region 20 thereof respectively are support ribs 26 of substantially constant thickness b, which are determined by axial planes E—passing radially through the longitudinal axis A of the pump—and which are inclined at an angle w of about 40° towards the longitudinal axis A of the pump. The cross-sectional height h of the support ribs 26 steadily increases in the longitudinal extent or in the axial direction away from the casing cover 18. The support ribs 26 are cast at the other end to a bearing cup 28 axially associated with the longitudinal axis A of the pump and an edge ring 30 which surrounds the bearing cup. An axial tubular portion 32 which is integral with the casing cover 18 connects the bearing cup 28 thereto, in centered relationship. The bearing cup 28, with its edge ring 30, and the support rings 26—of which there are four here—are also part of the casing cover 18 whose length a, approximately corresponds to a third of the pump length a.

Passing through the casing cover 18 and the rearward casing attachment portion 34—that is to say the bearing carrier casing 16—is a pump shaft 36 of a diameter d, while an impeller 40 is held on the front stepped end 37 thereof by a nut 38. The impeller 40 rotates in the spiral casing 14 which includes an intake or suction chamber 42, whose inlet in the region of the axial connecting flange 12 is identified by reference 43 and whose radial outlet in the connecting flange 12 _(a) is identified by reference 44. Disposed near the impeller 40 in the casing cover 18 is a stuffing-box packing 46 at the periphery of the cylindrical tubular portion 32. The internal space 29 of the bearing cup 28 is connected to the cylindrical tubular portion 32 which extends around the pump shaft 36 to form a heat barrier. If for example a flow agent of low viscosity at about 350° C. passes through the inlet 43, flow agent of higher viscosity at 130° C. is disposed in the internal space of the bearing cup.

The internal space 29 of the bearing cup 28, which adjoins the cylindrical tube portion 32, communicates with a sealing chamber 48 which is arranged in the bearing carrier casing 16 or in the casing attachment portion 34 and which is surrounded by an annular wall 50 and which is provided with at least one closure screw 52 together with a screwthreaded opening or passage 53 which accommodates the screw and which is inclined at an angle z of 45° relative to the longitudinal axis A of the pump, and with blade-like surface elements 55 which are inclined relative to each other and which each have a respective edge 54 parallel to the axis, the axial length e₁ thereof approximately corresponding to half the length e of the casing attachment portion 34. An outlet screw 52 _(b) towards the bottom is arranged in a radial opening or passage in the region of the chamber which is towards the bottom. In addition FIG. 2 shows a lateral closure screw 52 a which is required for venting when the pump 10 is used in a vertical position. A rear axial sliding ring seal 56—which is not relieved of load—can be seen in the sealing chamber 48.

Projecting from the annular wall 50 are four radial lugs 51 which are connected to corresponding counterpart lugs 51 _(a) of the edge ring 30 by screws 24 _(a). In embodiments which are not shown here—in particular of large dimensioning—an annular flange can also be provided, instead of the above-mentioned radial lugs 51. In order to increase the surface area of the outside of the annular wall, axially extending surface portions can be arranged on the outside of the annular wall.

The sliding ring seal 56 includes a coil spring 58—which is supported against a ring step or a ring 38 which is pushed on to the pump shaft 36—and which loads a rotating sliding ring 59 which with a stationary counterpart ring 60 forms a sealing gap. The counterpart ring 60 is disposed in the tubular space 62 of an axial shaped stub portion 64 of an axial length f which here corresponds approximately to half the sealing chamber length e₁. Arranged subsequently to the annular end part 65 of the stub portion 64 in the casing attachment portion 34 is a dish-like hollow space 66. Between the latter and the adjacent stepped shaft end 37 _(e) the pump shaft 36 is surrounded by a grooved-type ball bearing 68 with spacer disks 69 and a securing ring 70; that unit is covered by a bearing cover 72 of the casing attachment portion 34. Projecting radially beneath the latter is a plate-like support leg 74 which is fixed by screws 24 _(b), comprising an angle plate member, in opposite relationship to which, in the region of the spiral casing 14, are two supports 74 _(a) which project in parallel in eccentric relationship. The supports 74 _(a) and the support leg 74 are connected at the other end to a base plate (not shown).

Arranged in the internal space 29 in the bearing cup 28 in FIGS. 3 through 5 is a front hydrodynamic plain bearing 76 comprising a bearing bush 77 of a length g with an internal peripheral surface portion 78 of carbon material; the plain bearing 78, at its longitudinal center, is surrounded by a clamping or tolerance ring 80 of a width n, the ring 80 being provided in the bearing cup 28—that is to say at the housing side—; the ring 80 is of an elastic nature and force-lockingly connects the plain bearing 76 to the bearing cup.

The plain bearing 76 _(a) of the pump 10 _(a) as shown in FIGS. 6 and 7 has within the bearing bush 77 a coaxial bearing sleeve 82 and—besides the above-described outer tolerance ring 80 at the longitudinal center—two inner tolerance rings 80 _(i) of a width i which are disposed at the shaft side and which—viewed in longitudinal section—flank the outer tolerance ring 80 at the pump shaft 36 at a radial spacing on both sides. The width n of the outer tolerance ring 80 and the width i of the inner tolerance rings 80 _(i) are relatively short in relation to the length g of the bearing bush, for example the latter corresponds approximately to between five and six times the width i and n respectively.

Reference 84 in FIGS. 6 and 7 shows a nut which is disposed between the front plain bearing 76 _(a) and the rear sliding ring seal 56—which is here relieved of load—for the purposes of fixing the bearing sleeve 82. The sliding ring components for carrying the radial forces which occur preferably comprise silicon carbide in the illustrated embodiment.

The two above-discussed bearing types 76, 76 _(a) can also be used in the centrifugal pump 11 shown in FIGS. 8 through 12 in which the pump shaft 35 is in the form of a plug-in or stub shaft and is provided with an O-ring 88 within a shaft sleeve 86 of the sliding ring seal 56 _(a), the shaft sleeve 86 surrounding the pump shaft. The O-ring 88 is disposed between the pump shaft 35 and a shaft sleeve 89 embracing it.

At the rearward end of the bearing carrier casing 16 the pump shaft 35 includes a clamping ring 92 which carries a fan wheel 90 and which is surrounded towards the front by a protective grid 93 as protection to prevent articles from being poked in. The rearward shaft bearing—which is disposed in the motor—cannot be seen in the drawing.

The impeller 90 is surrounded by a wall ring 94—with apertured plate members 95—of a spacer 96 with endward flange rings 97, 97 _(a); they are connected by longitudinal ribs 98 which are parallel to the axis. The flange ring 97 which is at the right in the drawing is screwed to a parallel flange ring 99 of a motor 100, the flange ring 99 bearing against the spiral casing 14; the motor 100 is fixed by means of the spacer 96 to the pump 11.

In the configuration of a centrifugal pump 11 _(a) with a vertical shaft 35 as shown in FIG. 13 ff, the inlet 43 and the outlet 44 of the spiral casing 14 are on a straight diametral line Q. This pump 11 _(a) can also be provided with both of the described bearing forms 76, 76 _(a). 

1. A centrifugal pump, in particular a spiral-casing centrifugal pump, for a heat carrier medium, comprising a spiral casing (14) having an impeller (40), a casing cover (18) and an associated casing attachment portion (34) for a pump shaft (35, 36, 36 _(a)) provided with a shaft bearing (76, 76 _(a)) near the spiral casing (14) and a shaft seal (56) disposed at a spacing in relation to the shaft bearing in a sealing chamber (48), characterised in that a bearing cup (28) accommodating the shaft bearing (76, 76 _(a)), a tubular portion (32) surrounding the pump shaft (35, 36, 36 _(a)) as a heat barrier and support ribs (56) or the like profile elements arranged at a spacing relative to each other in the peripheral direction are parts of the casing cover (18).
 2. A centrifugal pump as set forth in claim 1 characterised in that the bearing cup (28) is held at an axial spacing towards the impeller (40) by the tubular portion (32) surrounding the pump shaft (35, 36, 36 _(a)).
 3. A centrifugal pump as set-forth in claim 1 or claim 2 characterised in that the casing attachment portion (34) attached to the casing cover (18) or an edge ring (30) carried by the support ribs (26) thereof delimits the sealing chamber (48) for the shaft seal (56).
 4. A centrifugal pump as set forth in claim 3 characterised in that at their ends remote from the base region (20) of the casing cover (18) the support ribs (26) are connected by the edge ring (30) surrounding the longitudinal axis (A) of the pump.
 5. A centrifugal pump as set forth in one of claims 1 through 4 characterised in that the support ribs (26) are inclined at an angle (w) to the longitudinal axis (A) of the pump from the base region (20) of the casing cover (18) towards the shaft seal (56).
 6. A centrifugal pump as set forth in claim 5 characterised by an angle (w) of between 30° and 60°.
 7. A centrifugal pump as set forth in one of claims 1 through 6 characterised in that the cross-sectional height (h) of the support ribs (26) which preferably extend in axial planes (E) passing radially through the longitudinal axis (A) of the pump increases towards the sliding ring seal (56).
 8. A centrifugal pump as set forth in one of claims 1 through 7 characterised in that the sealing chamber (48) adjoins the shaft bearing (76, 76 _(a)).
 9. A centrifugal pump as set forth in one of claims 1 through 8 characterised in that at least one abutment step (28) directed away from the spiral casing (24) for a further pump portion (96) is arranged at the casing cover (18).
 10. A centrifugal pump as set forth in claim 9 characterised in that the abutment step is a front ring (22) formed on the casing cover (18).
 11. A centrifugal pump as set forth in claim 9 or claim 10 characterised in that the abutment step or the front ring (22) projects from an annular flange (21) which surrounds the support ribs (26) and which is disposed at the transition thereof to a base region (20) of the casing cover (18).
 12. A centrifugal pump comprising a sealing ring (59) of the shaft seal which is in the form of a sliding ring seal (56), the sealing ring extending peripherally at a counterpart ring (60) provided at the housing side, as set forth in one of claims 1 through 11, characterised in that the counterpart ring (60) for the sealing ring (59) is arranged in a shaped stub portion (64) of the casing attachment portion (34), the stub portion projecting axially into the sealing chamber (48), and associated with the stub portion is at least one passage (58) inclined with respect to the longitudinal axis (A) of the pump, with a closure screw (52) closing the passage.
 13. A centrifugal pump as set forth in claim 12 characterised by an angle (z) between the longitudinal axis (A) of the pump and the longitudinal axis (B) of the passage (53) of about 45°.
 14. A centrifugal pump as set forth in claim 12 or claim 13 characterised by an axial length (f) of the stub portion (64) which corresponds approximately to half the axial length (e₁) of the sealing chamber (48).
 15. A centrifugal pump as set forth in one of claims 1 through 14 characterised in that the shaft bearing is in the form of a plain bearing (76) with a ratio of the length (g) of the bearing bush (77) to the diameter (d) of the pump shaft (35, 36, 36 _(a)) of between about 1.5 and 2.0, preferably about 1.8.
 16. A centrifugal pump as set forth in claim 15 characterised in that the bearing bush (77) of the plain bearing (76, 76 _(a)) is adapted to be dismantleable.
 17. A centrifugal pump as set forth in claim 15 or claim 16 characterised in that the plain bearing (76, 76 _(a)) or its bearing bush (77) is externally embraced approximately at its longitudinal center by a clamping or tolerance ring (80) which engages into the bearing cup (28).
 18. A centrifugal pump as set forth in claim 17 characterised in that the width (n) of the clamping or tolerance ring (80) corresponds to a fraction of the length (g) of the bearing bush (77).
 19. A centrifugal pump as set forth in claim 18 characterised in that the width (n) of the external clamping or tolerance ring (80) corresponds approximately to between a fifth and a sixth of the length (g) of the bearing bush (77).
 20. A centrifugal pump as set forth in one of claims 15 through 19 characterised in that the plain bearing (76 _(a)) includes an inner bearing sleeve (82) surrounded by a bearing bush (77) at the bearing cup side (FIGS. 6 and 7).
 21. A centrifugal pump as set forth in one of claims 15 through 20 characterised in that within the plain bearing (76 _(a)) the pump shaft (35, 36 _(a)) is embraced by at least one tolerance ring (80 _(i)) which engages into the pump shaft.
 22. A centrifugal pump as set forth in one of claims 17 through 21 characterised in that provided on respective sides of the outer tolerance ring (80), viewed in longitudinal section of the centrifugal pump (10 _(a)), is a respective inward tolerance ring (80 _(i)) which engages into the pump shaft (35, 36 _(a)).
 23. A centrifugal pump as set forth in one of claims 15 through 19 characterised in that the plain bearing (76) includes a bearing bush (77) at the bearing cup side, with a slidable internal peripheral surface portion (78) embracing the pump shaft (36).
 24. A centrifugal pump as set forth in claim 23 characterised by an internal peripheral surface portion (28) of the plain bearing (76) comprising carbon (FIGS. 4 and 5).
 25. A centrifugal pump as set forth in claim 23 or claim 24 characterised by a hardened pump shaft (36) or a corresponding shaft portion which is associated with the bearing bush (77).
 26. A centrifugal pump as set forth in one of claims 1 through 25 characterised in that the sliding ring seal (56) embraces a shaft sleeve (89) at the shaft side, wherein at least one O-ring (88) is provided between the shaft sleeve (89) and the pump shaft (36, 36 _(a)).
 27. A centrifugal pump as set forth in one of claims 1 through 26 characterised in that a rearward shaft bearing (68) for the pump shaft (36, 36 _(a)) is arranged in the casing attachment portion (34) at an axial spacing relative to the sliding ring seal (56) outside the sealing chamber (48).
 28. A centrifugal pump as set forth in claim 27 characterised in that at least one hollow space (66) is arranged between the sealing chamber (48) and the shaft bearing (68) in the casing attachment portion (34).
 29. A centrifugal pump as set forth in one of claims 1 through 28 characterised in that the pump shaft (36 _(a)) is in the form of a plug-in stub shaft with clamping ring (92).
 30. A centrifugal pump as set forth in one of claims 8 through 29 characterised in that the spiral casing (14) and the bearing carrier casing (16) are embraced by a spacer (96) which butts against the abutment step or steps or the front ring (22) respectively and it is attached to a motor (100). 